The invention relates to an arrangement for controlling the slip of an automatic friction clutch arranged between the engine and the gearbox of a motor vehicle. From another aspect, the invention relates to an arrangement for correcting data stored in a data memory for the control of such a friction clutch.
It is known to engage and disengage conventional friction clutches arranged between the engine and the gearbox of a motor vehicle by means of a positioning drive which adjusts the clutch as a function of a comparison between a desired value and an actual value to a position which can be predetermined by a desired position signal. The desired position signal is produced for the automatic operation of the clutch by control means according to the travel situation of the motor vehicle. The control means can adapt its engagement characteristic in a known manner to the differing requirements during the start up of the motor vehicle or during a change of gear speeds.
It is known from DE-A-34 38 594 to keep the slip of the clutch at a predetermined desired slip value by means of a slip controlling circuit, independent of the control means controlling engagement and disengagement of the clutch. The slip controlling circuit can be used, on the one hand, to reduce rotary vibrations in the power train of the motor vehicle in that, for example, as a function of the engine speed a slip which is slight in comparison with this speed is permitted. On the other hand, the slip controlling circuit can be made effective in the final phase of the engagement process in order to achieve particularly soft and smooth engagement.
With the known slip controlling circuit, the input speed and the output speed of the clutch are measured by means of speed sensors and an averaging circuit produces an average value signal corresponding to the timed average value of the difference between these speeds, which the slip controlling circuit compares with a signal representing the instantaneous difference. The slip controlling circuit produces the desired position signal adjusting the positioning drive as a function of this comparison. The accuracy of control of the known slip controlling circuit is frequently inadequate in practice if small speed differences between input speed and output speed of the clutch of, for example, 1 to 2% of the input speed are to be regulated. In particular, great variations in the differential speed can occur with the known slip controlling circuit during a change in the power requirement of the engine, for example owing to a change in the position of the accelerator pedal. The known slip controlling circuit can follow only to a limited extent and comparatively slowly during a change of load.